Electro-mechanical transducers and the fabrication thereof



mzamzisz J- V. COWAN SEARGH ROQM ELECTRO-MECHANICAL TRANSDUCERS AND THEFABRICATION THEREOF Original Filed Jan. 26. 1961 INVENTOR. V. (awn/7QQSJZW Patented Mar. 29, 1966 3.242.552 ELEC'IRO-MECRANMIAL TRANSDUCERSAND THE FABRECATION THEREOF John V. Cowan, Danbury, Conn., assignor toAutomation Industries, Inc, El Segundo, Calir'., a corporation ofCalifornia Original application Jan. 26, 196l, Ser. No. 35,103. nowPatent No. 3,192,420, dated .lune 29, I955. Divided and this applicationDec. 17, W64, Ser. No. 419,243 12 Claims. (Cl. 29--25.35)

This application is a division of co-pending applicationElectro-Mechanical Transducers and the Fabrication Thereof," Serial No.85,103, filed January 26, 1961, now Patent No. 3,192,420,. in the 'nameof John V. Cowan.

This invention relates to electro-mechnnical transducers and thefabrication thereof, and, more particularly, pertains to new andimproved transducers especially useful in ultrasonic inspectionapparatus.

In ultrasonic inspection, such as disclosed in US. Patent No. 2,398,701,it is sometimes desirable to introduce wave energy into a test object ata selected angle relative to a normal to the entering surface of theobject. This may be accomplished by tilting the transducer with respectto the entering surface and providing a wave energy coupling pathbetween the transducer and the entering surface by means of a liquid, asdisclosed in US. Patent No. 2.592.134 or 'by means of a solid material,as disclosed in US. Patent No. 2,527,986.

It is an object of the present invention to provide new and improvedelectro-mechanical transducers which may be employed to introduce waveenergy into a test object at an angle to normal without the need for anintervening coupling member.

A further object of the present invention is to provide new and improvedelectromechanical transducers which upon energization emit wave energyat an angle to a normal to a wave-emitting surface.

Yet another object of the present invention is to provide a new andimproved electromechanical transducer which upon energization emits waveenergy in a plurality of directions.

till another object of the present invention is to provide a new andimproved electromechanical transducer which upon energization emits ahighly focused beam of wave energy.

A further object of the present invention is to provide novel methods offabricating electromechanical transducers.

Another feature of the present invention is the provision of new andimproved apparatus for fabricating a novel transducer embodying theinvention.

Briefly stated, an electromechanical transducer embodying the presentinvention comprises a piezo-electric element having a pair ofsubstantially parallel surfaces and polarized at least in part along anaxis disposed at an angle other than ninety degrees relative to saidsurfaces.

A transducer of the foregoing type can be fabricated in accordance withthe invention by polarizing a polarizable piezo-electric element in agiven direction and extracting a section of the element having at leastone surface portion disposed at an angle other than ninety degreesrelative to the given direction.

Apparatus for fabricating an electromechanical trans ducer, according toanother feature of the invention, comprises a pair of electricalcontacts for engaging opposite surfaces of a piczo-clectric element, andmeans for displacing the contacts concomitantly relative to thepiezo-elcctric element while maintaining the contacts in pro-determinedorientation with respect to one another.

The novel features of the present invention are set forth in moreparticularity in the appended claims. The present invention, both as toits organization and manner of operation, together with further objectsand advantages thereof, may best be understood by reference to thefollowing description taken in connection with the accompanying drawingin which:

FIG. 1 is a schematic diagram of apparatus which may be employed infabricating an electromechanical transducer, the fabrication and thetransducer featuring individual aspects of the present invention.

FIG. 2 represents a manner of utilizing a new and improvedelectromechanical transducer of the type fabricated by the techniqueillustrated in FIG. 1;

FIGS. 3 and 4 illustrate modifications which may be employed in thetechnique of FIG. 1 to fabricate trans ducers in accordance with otherembodiments of the invention;

FIG. 5 is a perspective view of another form of appa-ratus which may beemployed to fabricate a transducer in accordance with the invention;

FIG. 6 is an enlarged view, partly in cross section, of a portion of theapparatus illustrated in FIG. 5; and

FIG. 7 is a perspective view of still another form of apparatus whichmay be employed to fabricate a trausducer in accordance with theinvention.

In FIG. 1, a large block 10 of a polarizable piezoeiectric material,such as lead zirconate, is shown to have parallel surfaces 11 and 12which are perpendicular to an axis X and to which electrodes 13 and 14are applied. Each of the electrodes may, for example, be composed ofsilver deposited in a. thin layer on the corresponding surfaces 11 and12. Electrical connections 15 and 16 extend from electrodes 13 and 14 toa source of polarizing potential comprised of a battery 17 connected toa potentiometer 18.

Element 10 is polarized by the application of a suitable potential fromsource 17, 18; preferably the element is maintained at an elevatedtemperature by means not shown. After polarization, the connections 15and 15 are broken thereby removing the polarizing potential. Of coursethe temperature of the element 10 is approximately reduced and itremains polarized along axis X. The process for polarization is wellknown and forms no part of the invention, thus a detailed description isunnecessary.

After polarization, a section is cut from element 10, as outlined bybroken lines 19 and 20 which define parallel surfaces of a transducerslab thereby extracted. Surfaces 19, 20 are oriented at an angle Arelative to axis X of some value other than ninety degrees.

As shown in FIG. 2, the slab defined by surfaces 19 and 20 is providedwith electrodes 21 and 22, such as thin layers of silver, to'whichelectrical loads 23 and 24 are connected. These leads extend toelectrical apparatus, for example, of the type disclosed in US. PatentNo. 2,398,701 thereby incorporating the transducer 19-22 in ultrasonicinspection apparatus. The transducer is placed in contact with a surface25 of a test object 26 and ultrasonic inspection of the test object isperformed. Of course, a suitable couplant liquid is employed in theusual way to provide a good acoustic path for ultrasonic wave energy.Also, if desired, the transducer may be damped in the usual manner. Inresponse to ultransonic signal energy, the transducer 19-22 producesultrasonic wave energy that passes into entering surface 25 along anaxis Y at an angle A with respect to a normal 2 to the surface 25. Itmay be seen from the foregoing description that an electromechanicaltransducer according to the present invention is adapted to emit waveenergy at an angle to a normal to a waveemitting surface thereof and anintervening coupling member is not needed.

In summary, an electro-mechanical transducer in accordance with thepresent invention is comprised of a piezzo-electric element defined byparallel surfaces 19, and polarized at least in part along an axis Ydisposed at an angle other than ninety degrees relative to surfaces 19and 20. The transducer further includes means comprised of electrodes 21and 22 and leads 23 and 24 for establishing electrical circuitconnections to surfaces 19 and 20.

In FIG. 3, a multisection element of, for example, lead zirconate, isutilized in order to provide different polarization directions. Theelement 30 has three sections including, for example, a central section31, having opposed surfaces 32 and 33 perpendicular to an axis Xintegral with end sections 34 and 35'. Section 34 has opposed surfaces36 and 37 perpendicular to an axis Y' and section 35 has opposedsurfaces 38 and 39 perpendicular to another axis Z. Axis Y forms anangle B relative to axis X while axis Z forms an angle C relative toaxis X. Angle C may, for example be equal to angle B, but of oppositesign. An electrode 40 extends along surfaces 36, 32 and 38 and anelectrode 41 extends along surface .57, 33 and 39. Electrical leads 15and 16 connect the electrodes 40 and 41 to potential source 17, 18(FIG. 1) so that the piezo-electric element 30 can be polarized. It isevident that polarization is effected along each of the axes X, Y and Zin sections 31, 34 and 35, respectively.

After polarization a continuous slab, defined by parallel broken lines42 and 43, is cut from element 30 and is utilized in the same manner asdescribed in connection with FIG. 2. It is evident that the transducerthus formed provides one beam normal to the entering surface of the testobject and two additional beams inclined at angles B and C to normal.

A focused transducer can be produced by utilizing a block 45 ofpolarizable piezo-electric material such as shown in FIG. 4. Block 45 isof generally frusto-conical configuration and includes parallel surfaces46 and 47 which are concentric relative to the center P of the cone.Electrodes 48 and 49 are disposed on surfaces 46 and 47 and areconnected by leads 15 and 16 to potential source 17, 18 for polarizingthe element 45. It is evident that polarization is effected along acentral axis X" and along radii extending from point P within the axesY" and Z".

After polarization a slab defined by parallel lines 50 and 51 which areperpendicular to axis-X" is cut from element 45 and the transducer slabis utilized in the same manner as the transducer slab illustrated inFIG. 2. From an inspection of FIG. 4 it is evident that the nature ofthe beam of wave energy from slab 50, 51 is such that effective focusingis achieved. Depending upon which of surfaces 50 and 51 is used tointroduce wave energy into a test object, the beam may be eitherdivergent or convergent. If desired, surfaces 46 and 47 may becylindrical instead of spherical.

A transducer may also be fabricated by means of apparatus illustrated inFIG. 5. A flat slab 55 of polarizable piezo-electric material hasparallel upper and lower surfaces 56 and 57 contacted by rollers 58 and59 of electrically conductive material. Each roller is supported at itsends by an individual one of fittings 60 that are mounted for slidingmovement in slots 61 and 62 of parallel arms 63 and 64.

As shown in FIG. 6, each fitting 60 is constructed of an electricallyinsulating material and includes a flat shank 65 received within itsslot, such as slot 61 in arm 63, for longitudinal sliding movement.Opposed heads 66 and 67 which are larger than the width of slot 61 holdthe fitting in place while permitting its sliding movement. A centralopening 68 receives a reduced diameter end portion 69 of contact roller58 for rotational movement.

Thus, the contact rollers 58 and 59 are supported by the arms 63 and 64for rotational movement as well as longitudinal movement along the arms.A tension spring 70 biases the rollers toward one another thereby tomaintain electrical contact with slab 55. Since all fittings areidentical, as thus far described, a detailed description of each isdeemed unnecessary.

An electrical brush 71 is in contact with the right-hand end of roller58 and a similar brush (not shown) contacts the corresponding portion ofroller 59. Leads 72 and 73 extend from the brushes to polarizingpotential source 17, 18 (FIG. 1). A suitable liquid couplant may beprovided for rollers 58 and 59 or the entire array may be immersed in ahigh dielectric liquid such as silicone oil.

Arms 63 and 64 are connected together by a cross rod 74 and by anothercross rod 75 which is pivotally supported by a bracket 76. The arms 63and 64 may thus be pivoted about the axis of rod 76 as the rollerstravel along surfaces 56 and 57 of element 55. It is evident that withthe foregoing arrangement, the axis of polarization extends in thedirection of the arms 63 and 64 and thus the polarization angle variesalong element 55. After polarization electrodes are provided for element55 and it is utilized as shown in FIG. 2.

An alternative mode of operation can be achieved by mounting the upperends of arms 63 and 64 on a carriage movable on tracks parallel tosurface 56 of element 55 while the arms are fixed at an adjustable anglerelative to that surface. The resulting polarization will be uniform andat the value to which the angle is adjusted.

Another form of apparatus for fabricating a transducer in accordancewith the invention is illustrated in FIG. 7. A disc 80 of polarizablepiezo-electric material is supported at its edge by a plurality ofrollers 81 constructed of an electrically insulating material. At leastone of the rollers 81 is driven so that disc 80 is rotated about itsrotational axis 82. A C-shaped member 83 of electrically insulatingmaterial straddles disc 80 and has a portion 84 extendingperpendicularly from one of its arms. Extension portion 84 is pivoted atits end to a fixed support 85 for pivoted movement about an axis 86which intersects axis 82. Electrode carriers 87 and 88 are suitablymounted on the ends of-the arms of C-shaped member 83 on opposite sidesof disc 80. The electrode carriers 87 and 88 are aligned with and springbiased toward one another and each carries a contact such as theconductive ball 89 illustrated for carrier 87.

In operation, a polarizing potential is applied to the electrodecarriers 87 and S8 and C-shaped member is tilted either manually orautomatically as disc 80 rotates about axis 82. Thus, ball 89 describesa spiral path on its associated surface of disc 80. Since thepolarization angle varies with the position of C-shaped member 83 withrespect to tilt axis 86, the resulting transducer will exhibit a waveenergy pattern of focused configuration.

Although lead zirconate has been specified, it is evi dent that anypiezo-clectric material polarizable by the application of a potentialmay be utilized in the practice of the invention such as barium titanateor lead metaniobate.

If desired, in the embodiment of FIGS. 1, 3 and 4, a block ofpolarizable material of suitable size may be employed so that one ormore sla-bs may be extracted.

It is to be understood that where reference is made to a transducer inits function of the conversion of electrical energy to wave energy, thetheorem of reciprocity applies, and the transducer exhibits the same orsimilar characteristics in its function of converting wave energy toelectrical energy.

While particular embodiments of the present invention have been shownand described, it is obvious that changes and modifications may be madewithout departing from this invention in its broader aspects and there-.fore, the aim in the appended claims is to cover all such changes andmodifications as wall within the true spirit and scope of thisinvention.

What is claimed is: 1. A method of fabricating an electro-mechanicaltrans ducer which comprises the steps of:

polarizing a polarizable piezo-electric element in a ft given direction;and

extracting a section of said piezoelectric element having at least onesurface portion disposed at an angle other than ninety degrees relativeto said given direction. 2. A method of fabricating aneiectrc-mechanical transducer which comprises the steps of:

applying a polarizing potential to a pair of coextensive surfaces of apolarizable piezo-electric element; and extracting a section of saidpiezoelectric element having at least one surface portion disposed at anangle to one of said coextensive surfaces.

3. A method of fabricating an eiectro-mechanical transducer whichcomprises the steps of:

applying a polarizing voltage to a pair of parallel surfaces of apolarizable piezo-electric element; and extracting a section of saidpiezo-electric element having parallel surfaces disposed at an anglerelative to said first-mentioned parallel surfaces. 4. A method offabricating an elecrro-mechanical transducer which comprises the stepsof:

forming a polarizable piezo-electric element to exhibit adjacentsections each having parallel surfaces, the surfaces of said sectionsbeing disposed at an angle relative to one another; applying apolarizing potential to corresponding pairs of parallel surfaces; and

extracting a portion of each of said sections thereof and havingsubstantially flat, parallel surfaces. 5. A method of fabricating anelectromechanical transducer which comprises the steps of:

forming a polarizable piezo-electric element to exhibit three adjacentsections each having parallel surfaces, and the surfaces of an outerpair of said sections being disposed at an angle relative to thesurfaces of a central section; applying a polarizing potential tocorresponding pairs of said parallel surfaces; and extracting a portionof said piezo-electric element extending through at least a part of eachof said sections thereof and having substantially fiat, parallelsurfaces. 6. A method of fabricating an electromechanical transducerwhich comprises the steps of:

forming a polarizable piezo-electric element to exhibit substantiallyparallel, curved surfaces; applying a polarizing potential to saidparallel surfaces; and extracting a portion of said piezo-elcctricelement having substantially fiat, parallel surfaces. 7. A method offabricating an electromechanical transducer which comprises the stepsof:

forming a polarizable piczo-electric element to exhibit substantiallyparallel, concentric spherically shaped surfaces; applying a polarizingpotential to said parallel surfaces; ard extracting a. portion of saidpiezo-electric element having substantially fiat, parallel surfaces. 8.A method of fabricating an electro-mechanical transducer which comprisesthe step of applying a polarizing potential to opposite surface portionsof a polarizable piezo-electric element, said opposite surface portionslying on radii of a cylinder having a center fixed relative to saidelement. 9. A method in accordance with claim 8 wherein said surfaceportions of said element lie in substantially fiat parallel planes andwherein said center of said cylinder is substantially parallel to one ofsaid planes. 10. Apparatus for polarizing an electro-mechanicaltransducer comprising: pivot arm means; support means for supportingsaid pivot arm means for pivotal movement; a pair of electricalcontacts; and means for supporting said electrical contacts on saidpivot arm means to one side of said support means for movement towardone another on a line along said pivot arm means. 11. Apparatusaccording to claim 10 wherein said pivot arm means includes a pair ofessentially straight arms, wherein said electrical contacts are in theform of cylindrical rollers, wherein said means for supporting saidelectrical contacts support adjacent ends of said cylindrical rollersfor rotation and for movement alor g a corresponding arm, and saidapparatus further comprising means for biasing said rollers toward oneanother. 12. Apparatus for polarizing an electro-mechanical transducercomprising:

a pair of electrical contacts for engaging opposite surfaces of apiezo-electric element; and means for displacing said contactsconcomitantly rela tive to the piezoelectric element while maintainingsaid contacts in predetermined orientation with respect to one another.

References Cited by the Examiner UNITED STATES PATENTS 2,602,101 7/1952Mesh 3l0-8.7 2,756,326 4/1955 Mason 310- 2,944,200 7/1960 Solomon317-462 WHITMORE A. WILTZ, Primary Examiner.

JOHN M. ROMANCHIK, Examiner.

1. A METHOD OF FABRICATING AN ELECTRO-MECHANICAL TRANSDUCER WHICHCOMPRISES THE STEPS OF: POLARIZING A POLARIZABLE PIEZO-ELECTRIC ELEMENTIN A GIVEN DIRECTION; AND EXTRACTING A SECTION OF SAID PIEZO-ELECTRICELEMENT HAVING AT LEAST ONE SURFACE PORTION DISPOSED AT AN ANGLE OTHERTHAN NINETY DEGREES RELATIVE TO SAID GIVEN DIRECTION.